Surface-modified zinc oxides

ABSTRACT

Surface-modified zinc oxides with a BET surface area of 18±5 m 2 /g and a C content of 0.1 to 5.0 wt. % are prepared by spraying the zinc oxides with the surface-modifying agent or adding this in vapour form and then heat-treating the mixture. They can be employed for the preparation of cosmetics.

The invention relates to surface-modified zinc oxides, a process fortheir preparation and their use.

One portion of the solar spectrum comprises wavelengths ofelectromagnetic energy which range between about 290 and 3,000 nm. Thisrange may be divided into different regions, namely:

1. the ultraviolet region (290-400 nm)

2. the visible region (400-760 nm) and

3. the near-infrared region (>760 nm).

The ultraviolet region has, moreover, been arbitrarily divided intothree bands, referred to as the UVA, UVB and UVC bands.

The UVB band extends from 290 to 320 nm. It is the principal cause ofthe sunburn reaction and it is also the most effective in stimulatingthe tanning reaction in the skin. UVC radiation (200-290=m) from the sundoes not reach the surface of the earth, although one can encounterradiation in this range from artificial sources such as germicidal lampsand high and low pressure mercury arc lamps. For purposes of the presentinvention however, protection against UVC radiation is generally not amajor concern, i.e., in contrast to the dangers posed by UVA and UVBradiation, The UVA band, which extends from 320-400 nm, can also causethe tanning reaction. UVA radiation can also cause sunburns, but itscapacity to do so is less than that of UVB radiation.

The amount of UVA radiation exposure, however, is increasing. This isdue to the fact that most sunscreens effectively block only UVBradiation. As stated above, UVB radiation is more capable than UVAradiation of causing the tanning and burning reactions. Therefore, ifone is using a sunscreen that blocks UVB radiation he/she will tend tostay in the sun for an extended period of time because the immediateeffects of the sun tan/burn are not evident. The problem is that UVA isstill penetrating the skin and although it is not causing anyimmediately obvious effects, it is causing long term damage. In recentyears, it has been well documented that UVA radiation, like UVBradiation, is harmful to the skin. In fact, current data reveal thatsolar radiation containing these wavelengths is the chief cause of skincancer, which presently accounts for 30-40% of all new cancers eachyear. In the United States alone, 500,000 new cases of skin cancer willbe reported this year and the number is expected to keep rising in thefuture. UVA radiation has been shown to promote skin cancer byinhibiting enzymes that repair cells damaged by UVB radiation. UVAradiation also penetrates more deeply into the skin than UVB radiationand causes changes in blood vessels and premature aging of the skin,thus adding to the damage produced by UVB rays (see, e.g., Hurwitz,Sidney, “The Sun and Sunscreen Protection: Recommendations for Children”Dermatol. Surg. Oncol; 14:6 (June 1988) P 657).

The goal of any sunscreen should thus be to protect the user from bothUVA and UVB radiation with a minimum of side effects. This end has notbeen adequately achieved with the use of presently available sunscreenproducts.

Sunscreen products can be grouped into two broad categories, i.e.,

1. topical sunscreens and

2. oral sunscreens.

The present invention focuses upon the topical sunscreens, which can befurther differentiated into two subcategories, namely

1. chemical sunscreens and

2. physical sunscreens.

Chemical sunscreens contain from about 3 to about 26% of one or moreUV-absorbing chemicals. When applied to the surface of the skin as athin film, i.e., about 10-15 μm in thickness, these chemicals act as afiller to diminish the penetration of UV radiation to the cells of theepidermis.

These sunscreens are typically applied in a cream, oil, lotion, alcoholor gel vehicle and they are usually colorless, because they do notcontain any visibly light-absorbing chemicals.

The most widely-used chemical sunscreens contain, for example,para-aminobenzoic acid (PABA), PABA esters (glyceryl PABA), amyldimethylPABA and octyldimethyl PABA), benzophenones (oxybenzone andsulisobenzone), cinnamates (octylmethoxy cinnamate and cinoxate),salicylates (homomethyl salicylate) and anthranilates.

To date, more than twenty-one such chemicals have been approved by theUnited States Food and Drug Administration as “safe and effective”agents in protecting skin against sunburn (see, e.g., Pathak, Madhu,“Sunscreens: Topical and Systemic Approaches for Protection of HumanSkin Against Harmful Effects of Solar Radiation”, Continuing MedicalEducation Series, J. Am. Acad. Dermat., 7:3 (September 1982) p. 285,291).

Questions have recently been raised, however, by the medical professionas to whether the chemical components of these sunscreens are indeedinert and further, whether repeated use of such sunscreens can result insignificant transdermal absorption of these chemicals. Because chemicalsunscreens are applied topically in relatively high concentrations(i.e., up to 26%), contact and photocontact sensitization can occur, aswell as hypersensitivity, i.e., photoallergic reactions (see Drumgoogleet al., “Sunscreening Agent Intolerance: Contact and PhotocontactSensitization and Contact Urticania” J. Am. Acad. Dermatol., 1990:22, p.1068).

Physical sunscreens, on the other hand, comprise particles of arelatively physiologically inert sunblock, i.e., UV-absorbing, compoundtypically suspended in a cream or lotion. Materials frequently utilizedfor this purpose include kaolin, talc and two metal oxides, i.e.,titanium dioxide and zinc oxide. The latter two compounds are notassociated with the inflammatory reactions noted above.

The physical sunscreen products are, however, typically messy andocclusive. Moreover, they additionally form a visible, colored (e.g.,white) layer on the surface of the skin, which is cosmeticallyunacceptable to many that are in need of sunscreen protection. Thiscauses many such individuals to forego the use of these products. Thecolor of these compositions is attributable to the optical properties ofthe particles from which these materials are formed. These propertiesare at least partially dependent upon the size of these particles, whichtypically have a fairly “standard” range of diameters, measured intenths of a micron (i.e., about greater than about 0.7-0.7μ).

In addition, presently available physical sunscreens are not easilywashed off of the user's body. Instead, they typically melt off with theheat of the sun, thus incidentally staining or otherwise discoloring theuser's clothing. Moreover, because they are applied as relatively thickfilms (20-50 μm), use of these products may also promote undesirableskin conditions, including miliaria, a skin disease caused by aninflammation of the sweat glands, and folliculitis, an inflammation ofthe hair follicle, As such, these physical sunscreen products are deemedcosmetically unacceptable by a large class of image conscious persons,which primarily includes young people. Unfortunately, this same group isthe exact population that needs solar protection the most.

It has stated that proper use of sunscreens prior to the age of 18 wouldprevent 80% of skin cancers (see e.g., Taylor et al.,“Photoaging/Photodamage and Photoprotection” 22 J. Am. Acad. Dermatol.,9 (1990).

In one variant of the “typical” prior art physical sunblocks describedabove, certain commercial sunscreen products containing titanium dioxideare made with what is known as “micronized” or “large surface area”particles of the metal oxide.

It should be noted here that the term “micronized” does not denote aspecific particle size. Rather, the term is only used to describe smallparticles having a large surface area. The titanium dioxide particlesutilized in these sunblock products have a diameter an order ofmagnitude smaller (i.e., measuring about 0.01μ) than the “standard”sized particles (measuring about greater than about 0.7-0.9μ) describedabove.

One drawback to the use of this material, however, is that titaniumdioxide absorbs neither as much UV-radiation nor transmits as muchvisible radiation as, for example, zinc oxide, which is utilized byapplicants in the present invention (see, e.g., Brown, Harvey E., ZincOxide: Properties and Applicants, pp. 11-12, FIG. 2-4 (1976)). Thus,although the use of micronized titanium dioxide particles does renderthe resultant product smoother and less occlusive, it does not obviatethe main drawback faced with the use of this material, i.e., itscomparatively lower effectiveness (in contrast to ZnO) as a sunblockagent.

Titanium dioxide-based products are also more opaque than those formedwith the zinc oxide of the present invention, which is due to the factthat the crystalline structure of the titanium dioxide material rendersit only partially transparent to visible wavelengths of light and thusnot generally as acceptable for cosmetic use.

Although it has been known to form micronized particles of zinc oxidefor very specialized uses in the rubber industry, these particlescontain substantial quantities (i.e., greater than about 200 ppm) oftrace metals such as lead, mercury, arsenic and cadmium. The potentialdangers to human health caused by exposure to these materials is welldocumented.

Thus, such zinc oxide particles containing these levels of trace metalsare not acceptable for topical application to human skin.

Greater public awareness of the harmful effects of exposure to excessivesolar radiation has therefore resulted in an increased use of sunscreenproducts by the public, coupled with a call for improved sunscreenmaterials free of the drawbacks described above by those whoselivelihood and/or leisure activities cause them to be exposed to anysubstantial amounts of solar radiation.

To avoid these problems a topical formulation for shielding skin fromultraviolet radiation is known which comprises:

-   -   a substantially colorless dermatologically acceptable liquid        carrier;    -   micronized particles of zinc oxide, said particles having an        average particle diameter of less than about 0.2 microns and        containg:        -   lead <20 ppm;        -   arsenic <3 ppm;        -   cadmium <15 ppm; and        -   mercury <1 ppm            said particles being substantially uniformly dispersed in            said substantially colorless dermatologically acceptable            liquid carrier to form a substantially visibly transparent            topical sunblock formulation, said particles being dispersed            in said carrier in an amount effective to shield skin over            which said substantially visibly transparent topical            sunblock formulation is applied from hazardous effects of            UVA and UVB radiation.

Zinc oxide is a reactive material which exhibits a wide range ofreactivity with alkaline as well as acidic solutions, liquids and gases.In some applications the reactive nature of the zinc oxide is desirable,for example in paint applications, the reactivity of the pigment resultsin adhesion into the polymer film. In many applications, it is highlydesirable to have zinc oxide in a non-reactive form, that is toeliminate, or make unavailable, the active sites present on themolecule.

Harvey Brown in his book Zinc Oxide Properties and Applications(International Lead Zinc Research Organization) states zinc oxidedisplays a high degree of reactivity in water with a wide range ofmaterials, including acids, acid salts, and alkaline materials. Many ofthe resulting compounds are complex structures because of the variety ofspecies furnished by zinc oxide in aqueous solution. Brown goes on tostate that zinc oxychloride, zinc phosphates, zinc silicates, and avariety of other materials can be formed in aqueous media.

One measure of the availability of reactive groups on the zinc oxide ispH change associated with use of zinc oxide. Zinc oxide containingreactive sites can increase the pH of aqueous products. In someinstances the increase can be from an initial pH of 7 to a pH of 8.7.This increase is not only a measure of the presence of reactive groups,but is highly undesirable in the formulation.

It is therefore very desirable to produce a zinc oxide, which has thepigment properties but lacks the reactivity found in untreated zincoxide.

One area in which zinc oxide has been used is in sunscreen products. Itprotects the skin from sun.

The traditional materials used for protecting the skin from the harmfuleffect of the sun are the organic sunscreens. These include para aminobenzoic acid and other materials, which absorb ultra violet light.Recently, studies have indicated that ultra violet light is a majorfactor in the ageing of skin. This has resulted in the incorporation ofsunscreens in products, which are not aimed specifically for use at thebeach, like make up. Additionally, there has been an increased interestin providing higher levels of protection to the skin.

The called SPF system has been developed to evaluate various materialsfor their effectiveness in protecting the skin from the damaging affectsof the sun. The quest for higher and higher SPF values has resulted inthe use of greater levels of organic sunscreen. These materials have atendency to be irritating at high concentrations, and have the affect ofincreasing the available organic material for bacteria. This result inthe need for more preservative to protect the higher level of organicsun screen agent from bacterial degradation. The higher levels ofpreservative result in higher irritation levels, which can be addressedby incorporation of irritation mitigates, which themselves are degradedby bacteria.

The use of inorganic sunscreen agents like zinc oxide is a good wayaround the use of organic sunscreens, since they are not attacked bybacteria. However, their use does have some other inherent problems.Specifically, these materials are not easily formulated into stableproducts, due to the reactivity issues raised above. Zinc oxide tends toagglomerate in many finished formulations, loosing it's effectiveness inthe formulation and resulting in unacceptable aesthetic results, mostcommonly whitening and viscosity changes. Additionally, zinc oxide tendsto raise the pH of the formulation to about 8.5, which is too high formany skin care formulations. These formulations tend to be useful at apH of 6-7. Zinc oxide has limited usefulness as is due to theseproblems.

One approach has been to pre-disperse the zinc oxide in an organic oillike Siltech's patented tri-(octyldodecyl)citrate. While the dispersionis fairly stable, the coating is not permanent since there is noreaction between the oil and the zinc oxide. The oil also disrupts theuniformity of the zinc oxide on the skin. Traditionally, dispersing aidshave been added to formulations to minimize the disruptive effect uponthe film. These include phosphate esters, and lecithin. These too sufferfrom the labile nature of the surface treatment and dissociation betweenthe particle and the oil. This is especially evident when zinc oxide isexposed to extreme mechanical or thermal stress as in the production ofplastics or stick cosmetics.

It is known to overcome the shortfalls of zinc oxide by reacting aspecific silicone compound under controlled conditions to produce astable, surface treated zinc oxide which maintains it's state ofdispersions and does not contribute significantly to chemicalinstability in the formulations.

According to U.S. Pat. No. 5,486,631 it has been found that highlyeffective system for hydrophobizing zinc oxide makes use of a siliconecompound conforming to the following structure:

Me is methyl;R is alkyl having one to ten carbon atoms;R′ is methyl or ethyl;a is an integer ranging from 4 to 12.

The known process for hydrophobizing zinc oxide and the resultanthydrophobic zinc oxide show the disadvantage that the hydrophobazingagent produces a polymerized cover on the surface of the zinc oxide.

It is one object of the invention to overcome the disadvantage of theknown hydrophobic zinc oxide.

The invention provides surface-modified zinc oxides, which arecharacterized in that they have the following physico-chemicalcharacteristic data:

BET surface area: 18±5 m²/g

C content: 0.1 to 5.0 wt. %

The surface-modified zinc oxides according to the invention canfurthermore have a loss on drying of 0.1 to 0.2% and a loss on ignitionof 0.8 to 1.4.

The surface-modified zinc oxide according to the invention preferablyhas defined molecular groups on the surface.

The invention also provides a process for the preparation of thesurface-modified zinc oxides according to the invention, which ischaracterized in that the zinc oxides, optionally after spraying withwater, are sprayed with the surface-modifying agent at room temperatureand the mixture is then heat-treated at a temperature of 50 to 400° C.over a period of 1 to 6 h.

Alternatively, the surface-modified zinc oxides according to theinvention can be prepared by treating the zinc oxides, optionally afterspraying with water, with the surface-modifying agent in vapour form andthen heat-treating the mixture at a temperature of 50 to 800° C. over aperiod of 0.5 to 6 h.

The heat treatment can be carried out under an inert gas, such as, forexample, nitrogen.

The surface modification can be carried out continuously or batchwise inheatable mixers and dryers with spray devices. Suitable devices can be,for example: plough share mixers or plate, fluidized bed or flow-beddryers.

Any desired zinc oxide can be employed as the hydrophilic zinc oxide.For example, a zinc oxide which is known from WO 92/13517 can beemployed. A zinc oxide which is described in the earlier Applicationaccording to DE 102 12 680 can preferably be employed.

This zinc oxide is a nanoscale, pyrogenically produced zinc oxide powderhaving a BET surface area of 10 to 200 m²/g, characterised in that it isin the form of aggregates of anisotropic primary particles and that theaggregates display an average diameter of 50 to 300 nm.

The primary particles are understood to be the smallest particles inhigh-resolution TEM images, which are obviously unable to be broken downany further. Several primary particles can congregate at their points ofcontact to form aggregates. These aggregates are either impossible orvery difficult to break down again using dispersing devices. Severalaggregates can join together loosely to form agglomerates, whereby thisprocess can be reversed again by suitable dispersion.

The term anisotropic means that the arrangement of atoms differs alongthe three spatial axes. Anisotropic primary particles include forexample those that are acicular, nodular or platelet-shaped. A cubic orspherical arrangement, for example, would be isotropic.

Pyrogenic refers to the formation of oxides by flame oxidation of metalsor non-metals or compounds thereof in the gas phase in a flame producedby reaction of a fuel gas, preferably hydrogen, and oxygen. Highlydisperse, non-porous primary particles are initially formed which, asthe reaction continues, coalesce to form aggregates, and these cancongregate further to form agglomerates.

In a particular embodiment the aggregates can comprise a mixture ofnodular primary particles and acicular primary particles, whereby theratio of nodular to acicular primary particles can be between 99:1 and1:99.

The nodular primary particles preferably display an average diameter of10 to 50 nm and the acicular primary particles preferably display alength of 100 nm to 2000 nm and a width of 10 nm to 100 nm.

The aggregates in the powder can display a largely anisotropicstructure, defined by a shape factor F(circle) of below 0.5. Thevariable F(circle) describes the deviation of an aggregate from aperfect circular shape. In a perfect circular object F(circle) equals 1.The lower the value, the further removed the object structure from theperfect circular shape. The parameter is defined according to ASTM3849-89.

The powder can display at its surface an oxygen concentration asnon-desorbable moisture in the form of Zn—OH and/or Zn—OH₂ units of atleast 40%. It is determined by XPS analysis (XPS=X-ray photoelectronspectroscopy) of the oxygen signals at 532 to 533 eV and 534 to 535 eV.

The powder can preferably display a transmission of no more than 60% ata wavelength of 310 nm and 360 nm.

In a particular embodiment the bulk density of the powder is 40 to 120g/l.

Te production of the powder is characterised in that zinc powder isconverted into zinc oxide powder in four successive reaction zones,evaporation zone, nucleation zone, oxidation zone and quench zone,

-   -   whereby in the evaporation zone the zinc powder conveyed there        by an inert gas stream is evaporated in a flame of air and/or        oxygen and a fuel gas, preferably hydrogen, under the proviso        that the reaction parameters are chosen such that oxidation of        the zinc does not occur,    -   and whereby in the nucleation zone, where the hot reaction        mixture, consisting of zinc vapour, water vapour as a reaction        product of the flame reaction and optionally excess fuel gas,        arrives from the evaporation zone, it cools to temperatures        below the boiling point of zinc or is cooled by means of an        inert gas,    -   and whereby in the oxidation zone the mixture from the        nucleation zone is oxidised with air and/or oxygen,    -   and whereby in the quench zone the oxidation mixture is cooled        to temperatures of below 400° C. by addition of cooling gas (for        example nitrogen, air, argon, carbon dioxide).

The process can be performed in such a way that in the evaporation zonean excess of fuel gas is used, expressed in lambda values of 0.5 to0.99, preferably 0.8 to 0.95.

In a particular embodiment the process can be performed in such a waythat the temperature in the evaporation zone is preferably between 920°C. and 2000° C. In the nucleation zone the temperature can preferably bebetween 500° C. and 900° C., particularly preferably between 700° C. and800° C.

Furthermore the cooling rate

-   -   in the nucleation zone can preferably be between 100        Kelvin/seconds and 10000 Kelvin/seconds, particularly preferably        between 2000 Kelvin/seconds and 3000 Kelvin/seconds and    -   in the quench zone the cooling rate can preferably be between        1000 Kelvin/seconds and 50000 Kelvin/seconds, particularly        preferably between 5000 Kelvin/seconds and 15000 Kelvin/seconds.

The residence time of the reaction mixture in the

-   -   evaporation zone can preferably be between 0.1 seconds and 4        seconds, preferably between 0.5 seconds and 2 seconds,    -   in the nucleation zone between 0.05 seconds and 1.00 seconds,        preferably between 0.1 seconds and 0.2 seconds,    -   in the oxidation zone between 5 milliseconds and 200        milliseconds, preferably between 10 milliseconds and 30        milliseconds,    -   and in the quench zone between 0.05 seconds and 1.00 seconds,        preferably between 0.1 seconds and 0.2 seconds.

The process can also be performed in such a way that air and/or oxygenand the fuel gas can be supplied to one or more points within theevaporation zone.

The zinc oxide powder can be separated from the gas stream by means of afilter, cyclone, washer or other suitable separators.

The following compounds can be employed as the surface-modifying agent:

-   a) Organosilanes of the type (RO)₃Si(C_(n)H_(2n+1)) and (RO)₃Si    (C_(n)H_(2n−1))    -   R=alkyl, such as, for example, methyl-, ethyl-, n-propyl-,        i-propyl-, butyl-    -   n=1-20-   b) Organosilanes of the type R′_(x)(RO)_(y)Si(C_(n)H_(2n+1)) and    R′x(RO)_(y)Si(C_(n)H_(2n−1))    -   R=alkyl, such as, for example, methyl-, ethyl-, n-propyl-,        i-propyl-, butyl-    -   R′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-,        i-propyl-, butyl-    -   R′=cycloalkyl    -   n=1-20    -   x+y=3    -   x=1,2    -   y=1,2-   c) Halogeno-organosilanes of the type X₃Si(C_(n)H_(2n+1)) and X₃Si    (C_(n)H_(2n−1))    -   X=Cl, Br    -   n=1-20-   d) Halogeno-organosilanes of the type X₂(R′)Si(C_(n)H_(2n+1)) and    X₂(R′)Si(C_(n)H_(2n−1))    -   X=Cl, Br    -   R′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-,        i-propyl-, butyl-    -   R′=cycloalkyl    -   n=1-20-   e) Halogeno-organosilanes of the type X(R′)₂Si(C_(n)H_(2n+1)) and    X(R′)₂Si(C_(n)H_(2n−1))    -   X=Cl, Br    -   R′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-,        i-propyl-, butyl-    -   R′=cycloalkyl    -   n=1-20-   f) Organosilanes of the type (RO)₃Si(CH₂)_(m)—R′    -   R=alkyl, such as methyl-, ethyl-, propyl-    -   m=0,1-20    -   R′=methyl-, aryl (for example —C₆H₅, substituted phenyl        radicals)        -   —C₄F₉, OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂        -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂        -   —OOC(CH₃)C═CH₂        -   —OCH₂—CH(O)CH₂        -   —NH—CO—N—CO—(CH₂)₅        -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)_(3 —S)            _(x)—(CH₂)₃Si(OR)₃        -   —SH        -   —NR′R″R′″ (R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl,            aryl, benzyl, C₂H₄NR′″ R′″″ where R″″═H, alkyl and R′″″═H,            alkyl)-   g) Organosilanes of the type (R″)_(x)(RO)_(y)Si(CH₂)_(m)—R′    -   R″=alkyl x+y=2        -   =cycloalkyl x=1,2            -   y=1,2            -   m=0,1 to 20    -   R′=methyl-, aryl (for example —C₆H₅, substituted phenyl        radicals)        -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂        -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂        -   —OOC(CH₃)C═CH₂        -   —OCH₂—CH(O)CH₂        -   —NH—CO—N—CO—(CH₂)₅        -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃,            —NH—(CH₂)₃Si(OR)₃—S_(x)—(CH₂)₃Si(OR)₃        -   —SH        -   —NR′R″R′″ (R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl,            aryl, benzyl, C₂H₄NR″″R′″″ where R″″═H, alkyl and R′″″═H,            alkyl)-   h) Halogeno-organosilanes of the type X₃Si(CH₂)_(m)—R′    -   X=Cl, Br    -   m=0,1-20    -   R′=methyl-, aryl (for example —C₆H₅, substituted phenyl        radicals)        -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂        -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂        -   —N—(CH₂—CH₂—NH₂)₂        -   —OOC(CH₃)C═CH₂        -   —OCH₂—CH(O)CH₂        -   —NH—CO—N—CO—(CH₂)₅        -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃,            —NH—(CH₂)₃Si(OR)₃—S_(x)—(CH₂)₃Si(OR)₃        -   —SH-   i) Halogeno-organosilanes of the type (R)X₂Si(CH₂)_(m)—R′    -   X=Cl, Br    -   R=alkyl, such as methyl, -ethyl-, propyl-    -   m=0,1-20    -   R′=methyl-, aryl (e.g. —C₆H₅, substituted phenyl radicals)        -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂—NH₂, —N₃, —SCN,            —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂        -   —OOC(CH₃)C═CH₂        -   —OCH₂—CH(O)CH₂        -   —NH—CO—N—CO—(CH₂)₅—NH—COO—CH₃, —NH—COO—CH₂—CH₃,            —NH—(CH₂)₃Si(OR)₃,        -   wherein R can be methyl-, ethyl-, propyl-, butyl-        -   —S_(x)—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,            propyl-, butyl-        -   —SH-   j) Halogeno-organosilanes of the type (R)₂XSi(CH₂)_(m)—R′    -   X=Cl, Br    -   R=alkyl    -   m=0,1-20    -   R′=methyl-, aryl (e.g. —C₆H₅, substituted phenyl radicals)        -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂—NH₂, —N₃, —SCN,            —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂        -   —OOC(CH₃)C═CH₂        -   —OCH₂—CH(O)CH₂        -   —NH—CO—N—CO—(CH₂)₅        -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃,            —NH—(CH₂)₃Si(OR)₃—S_(x)—(CH₂)₃Si(OR)₃        -   —SH-   k) Silazanes of the type    -   R=alkyl, vinyl, aryl    -   R′=alkyl, vinyl, aryl    -   1) Cyclic polysiloxanes of the type D 3, D 4, D 5, wherein D 3,        D 4 and D 5 are understood as cyclic polysiloxanes with 3, 4 or        5 units of the type —O—Si(CH₃)₂—. E.g.        octamethylcyclotetrasiloxane=D 4-   m) Polysiloxanes or silicone oils of the type-   R=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as    phenyl und substituted phenyl radicals, (CH₂)_(n)—NH₂, H-   R′=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as    phenyl- and substituted phenyl radicals, (CH₂)_(n)—NH₂, H-   R″=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as    phenyl- and substituted phenyl radicals, (CH₂)_(n)—NH₂, H-   R′″=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as    phenyl und substituted phenyl radicals, (CH₂)_(n)—NH₂, H

The surface-modified zinc oxides according to the invention can be usedfor the preparation of cosmetics, in particular for the preparation ofsuncreen compositions.

The surface-modified zinc oxides according to the invention have thefollowing advantages:

They show as synergistic effect with cosmetic indredients when used assunprotecting agents.

EXAMPLES

Analytical Methods

The BET surface area is determined according to DIN 66131.

The transmission electron micrographs were obtained with a Hitachitransmission electron microscope, model H-75000-2. Approximately 500 to600 aggregates were analysed by means of the CCD camera in thetransmission electron microscope.

The variable F(shape) equals the quotient of the minimum to the maximumaggregate diameter. The variable F(circle) is calculated asF(circle)=4n×average surface area)/2 (P), where P=circumference of theaggregates.

The variables F(shape) and F(circle) describe the deviation of aparticle from a perfect circular shape. F(shape) and F(circle) are 1 fora perfect circular object. The lower the value, the further removed theobject structure from the perfect circular shape.

The parameters are defined according to ASTM3849-89.

The surface properties are determined by large-area (1 cm²) XPS analysis(XPS=X-ray photoelectron spectroscopy), both in the original conditionand after 30 minutes' surface erosion by ionic bombardment (5 keV argonions). Fine structures of the oxygen signals are determined byGaussian/Lorentzian curve analyses for oxygen.

One-percent aqueous solutions are used for the transmissionmeasurements. Dispersion is performed by means of an ultrasonicinstrument from Bandelin Elektronik. The sonication period is oneminute. The measurements are taken using a Perkin Elmer Lambda 2 UV/VisSpectrometer.

The bulk density was determined in accordance with DIN-ISO 787/XI.

Examples

FIG. 1 shows a flow diagram of the process according to the inventionwith the process stages and the incoming and outgoing mass flows.

There is: I=evaporation; II=nucleation; III=oxidation; IV=quenching;A=zinc oxide powder+inert gas; B=zinc vapour, water, (fuel gas); C=Zincparticles, water, (inert gas, fuel gas); D=zinc oxide particles, water,(inert gas); a=fuel gas, air/O₂; b=cooling (inert gas); c=air/O₂;d=cooling gas.

Example 1

Zinc powder (250 g/h, particle size=5 μm) is conveyed by means of anitrogen stream (1.5 m³/h) into an evaporation zone, where ahydrogen/air flame (hydrogen: 4.25 m³/h, air: 8.40 m³/h, lambda=0.82) isburning. The zinc powder is evaporated here. The reaction mixtureconsisting of zinc vapour, hydrogen, nitrogen and water is then cooledto a temperature of 850° C. by the addition of 1 m³/h nitrogen. 5 m³/hoxidation air and 34 m³/h quench air are then added, whereby thereaction temperature falls to values below 400° C. The zinc oxide powderobtained is separated from the gas stream by filtration.

Example 2

Same as Example 1, whereby the parameters are altered to the valuesshown in Table 1.

Example 3 (Comparative Example)

Same as Example 1, except with an excess of air compared to oxygen inthe evaporation zone. The parameters are altered to the values shown inTable 1.

Example 4 (Comparative Example)

Same as Example 1, except with no nucleation zone, the temperature priorto oxidation does not fall below the boiling point of zinc. Theparameters are altered to the values shown in Table 1.

The characterisation of the products obtained from these examples isshown in Table 2.

Evaluation of the image analysis reveals the clearest differencesbetween the zinc oxide powders according to the invention and the priorart for the average surface area of the particles, the aggregate sizesand the shape factor F(circle).

XPS analyses were performed of the zinc oxide powders according to theinvention from Examples 1 and 2. It was found that the moisture contentas non-desorbable oxygen in the form of Zn—OH and Zn—OH₂ units is 55.5%(Example 1) and 48.3% (Example 2). The moisture is thus significantlyhigher for example in the Nanotek Zinc Oxide product from NanophaseTechnologies.

FIG. 2 shows a transmission electron micrograph of the powder accordingto the invention. Aggregates of nodular and acicular aggregates canclearly be seen. TABLE 1 Process parameters Example 1 Example 2 Example3⁽¹⁾ Example 4⁽¹⁾ Evaporation Zinc g/h 250 300 300 250 Nitrogen m³/h 1.51.5 1.0 2 Hydrogen m³/h 4.3 4.6 5 4.5 Air m³/h 8.4 9.0 22 20.5 Lambda0.82 0.84 1.8 1.9 Nucleation Cooling gas m³/h 1 1.5 1 0.5 Temperature °C. 850 870 1050 960 Oxidation Oxidation air m³/h 5.0 4.0 4 — QuenchingQuench gas m³/h 34.0 30.0 10 — Temperature ° C. 285 296 424 526⁽¹⁾Comparative example

TABLE 2 Product properties Example 1 Example 2 Example 3⁽¹⁾ Example 4⁽¹⁾BET surface area m²/g 36 20 7.5 16 Average surface area nm² 5306 1576261070 3220219 Average aggregate nm 75 133 186 515 diameter Averageprimary nm 17 24 43 79 particle size Shape factor F(shape) 0.61 0.610.59 0.62 Shape factor 0.37 0.32 0.43 0.65 F(circle) Bulk density g/l 8062 90 100 Transmission % 50 56 60 66 Morphology Predominantly AggregatesNon-aggregated Predominantly nodular consisting of needles and needles,non- aggregates needles and tetrahedra aggregated nodules⁽¹⁾Comparative exampleSurface Modification

For the surface modification, the zinc oxides are initially introducedinto a mixer and, with intensive mixing, optionally first sprayed withwater and then sprayed with the surface-modifying agent. When thespraying has ended, after-mixing can be carried out for a further 15 to30 min, and then heat treatment for 1 to 4 h at 50 to 400° C.

The water employed can be acidified with an acid, for examplehydrochloric acid, down to a pH of 7 to 1. The silanizing agent employedcan be dissolved in a solvent, such as, for example, ethanol. TABLE 1Surface modification of the zinc oxide preparation Example 1 2 3 OxideZnO ZnO ZnO Surface-modifying octyl- octyl- polydi- agent trimethoxy-trimethoxy- methyl- silane silane siloxane Parts of surface- 1.5 3 2modifying agent/100 parts of oxide Parts of H₂O/100 0 0.2 0 parts ofoxide Temperature [° C.] 120 120 350 Temperature time [h] 2 2 2

TABLE 2 Physico-chemical data of the surface-modified products fromtable 1 Example 1 2 3 BET surface area [m²/g] 18 18 17 C content [%] 0.60.9 0.6 Loss on drying [%] 0.1 0.1 0.2 Loss on ignition [%] 0.9 1.4 0.8pH 6.5 6.8 7.3

Use Examples

The formulations according to the invention which, in the combination ofZnO (w.c.=coating=Trimethoxyoctylsilane), have shown a synergisticeffect with either OC=Octocrylene, OMC=Ethylhexyl Methoxycinnamate,PISA=Phenylbenzimidazole Sulfonic Acid or BEMT=Bis-EthylhexyloxyMethoxyphenyl Triazine are summarized in the following.

For statistical reasons it is assumed that the SPF should be greaterthan or equal to two units higher than the total SPF of the individualformulations if synergism is to be referred to.

The SPF (sun protection factor) measurements are carried out in vitrowith an Optometrics SPF 290-S apparatus.

Examples 1-3

The standard recipe for W/O emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theoily phase (Ethylhexyl Stearate and Mineral Oil).

-   1 Standard recipe W/O emulsion with ZnO (w.c.)-   2 Standard recipe W/O emulsion with OC

3 Standard recipe W/O emulsion with ZnO (w.c.) and OC TABLE 3 Build-upof the W/O recipes in examples 1-3 (data in %) Phase INCI 1 3 4 A CetylPEG/PPG −10/1 2.5 2.5 2.5 Dimethicone Ethylhexyl Stearate 12.5 12.5 10.0Mineral Oil 12.5 12.5 10.0 Isostearic Acid 1.0 1.0 1.0 HydrogenatedCastor Oil 0.5 0.5 0.5 Microcrystalline Wax 1.0 1.0 1.0 Octocrylene 5.05.0 Zinc Oxide (w.c.) 5.0 5.0 Zinc Oxide (w/o.c.) B Sodium Chloride 0.50.5 0.5 Aqua 64.45 64.45 64.45 2-Bromo-2-Nitropropane- 0.05 0.05 0.051,3-diol SPF 2 3 6

Examples 4-7

The standard recipe for O/W emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theaqueous phase (Aqua). Isostearic acid is employed experimentally as asurface modifier and pH stabilizer.

-   4 Standard recipe O/W emulsion with ZnO (w.c.)-   5 Standard recipe O/W emulsion with OC-   6 Standard recipe O/W emulsion with ZnO (w.c.) and OC

7 Standard recipe O/W emulsion with ZnO (w.c.), OC and isostearic acidTABLE 4 Build-up of the O/W recipes in examples 4-7 (data in %) PhaseINCI 4 5 6 7 A Ceteareth-15, 2.5 2.5 2.5 2.5 Glyceryl Stearate GlycerylStearate 1.0 1.0 1.0 1.0 Stearyl Alcohol 2.0 2.0 2.0 2.0 C12-15 Alkyl14.5 9.5 9.5 8.5 Benzoate Octocrylene 5.0 5.0 5.0 Zinc Oxide (w.c.) 10.010.0 10.0 Zinc Oxide (w/o.c.) Isostearic Acid 1.0 B Glycerine 3.0 3.03.0 3.0 Aqua 66.5 76.5 66.5 66.5 Chloroacetamide 0.1 0.1 0.1 0.1 CXanthan Gum 0.4 0.4 0.4 0.4 SPF 2 3 8 9

Examples 8-10

The standard recipe for W/O emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theoily phase (Ethylhexyl Stearate and Mineral Oil).

-   8 Standard recipe W/O emulsion with ZnO (w.c.)-   9 Standard recipe W/O emulsion with OMC

10 Standard recipe W/O emulsion with ZnO (w.c.) and OMC TABLE 5 Build-upof the W/O recipes in examples 8-10 (data in %) Phase INCI 8 9 10 ACetyl PEG/PPG −10/1 Dimethicone 2.5 2.5 2.5 Ethylhexyl Stearate 12.512.5 10.0 Mineral Oil 12.5 12.5 10.0 Isostearic Acid 1.0 1.0 1.0Hydrogenated Castor Oil 0.5 0.5 0.5 Microcrystalline Wax 1.0 1.0 1.0Ethylhexyl Methoxycinnamate 5.0 5.0 Zinc Oxide (w.c.) 5.0 5.0 Zinc Oxide(w/o.c.) B Sodium Chloride 0.5 0.5 0.5 Aqua 64.45 64.45 64.452-Bromo-2-Nitropropane-1,3-diol 0.05 0.05 0.05 SPF 2 7 13

Examples 11-14

The standard recipe for O/W emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theaqueous phase (Aqua). Isostearic acid is employed experimentally as asurface modifier and pH stabilizer.

-   11 Standard recipe O/W emulsion with ZnO (w.c.)-   12 Standard recipe O/W emulsion with OMC-   13 Standard recipe O/W emulsion with ZnO (w.c.) and OMC

14 Standard recipe O/W emulsion with ZnO (w.c.), OMC and isostearic acidTABLE 6 Build-up of the O/W recipes in examples 11-14 (data in %) PhaseINCI 11 12 13 14 A Ceteareth-15, Glyceryl 2.5 2.5 2.5 2.5 StearateGlyceryl Stearate 1.0 1.0 1.0 1.0 Stearyl Alcohol 2.0 2.0 2.0 2.0 C12-15Alkyl Benzoate 14.5 9.5 9.5 8.5 Ethylhexyl Methoxycinnamate 5.0 5.0 5.0Zinc Oxide (w.c.) 10.0 10.0 10.0 Zinc Oxide (w/o.c.) Isostearic Acid 1.0B Glycerine 3.0 3.0 3.0 3.0 Aqua 66.5 76.5 66.5 66.5 Chloroacetamide 0.10.1 0.1 0.1 C Xanthan Gum 0.4 0.4 0.4 0.4 SPF 2 6 11 16

Examples 15-17

The standard recipe for W/O emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theoily phase (Ethylhexyl Stearate and Mineral Oil).

-   15 Standard recipe W/O emulsion with ZnO (w.c.)-   16 Standard recipe W/O emulsion with PISA

17 Standard recipe W/O emulsion with ZnO (w.c.) and PISA TABLE 7Build-up of the W/O recipes in examples 15-17 (data in %) Phase INCI 1516 17 A Cetyl PEG/PPG −10/1 Dimethicone 2.5 2.5 2.5 Ethylhexyl Stearate12.5 15.0 12.5 Mineral Oil 12.5 15.0 12.5 Isostearic Acid 1.0 1.0 1.0Hydrogenated Castor Oil 0.5 0.5 0.5 Microcrystalline Wax 1.0 1.0 1.0Zinc Oxide (w.c.) 5.0 5.0 Zinc Oxide (w/o.c.) B Sodium Chloride 0.5 0.50.5 Aqua 64.45 49.45 49.45 2-Bromo-2-Nitropropane-1,3-diol 0.05 0.050.05 Phenylbenzimidazole Sulfonic 15.0 15.0 Acid (20% Aqua) SPF 2 5 9

Examples 18-21

The standard recipe for O/W emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theaqueous phase (Aqua). Isostearic acid is employed experimentally as asurface modifier and pH stabilizer.

-   18 Standard recipe O/W emulsion with ZnO (w.c.)-   19 Standard recipe O/W emulsion with PISA-   20 Standard recipe O/W emulsion with ZnO (w.c.) and PISA

21 Standard recipe O/W emulsion with ZnO (w.c.), PISA and isostearicacid TABLE 8 Build-up of the O/W recipes in examples 18-21 (data in %)Phase INCI 18 19 20 21 A Ceteareth-15, Glyceryl Stearate 2.5 2.5 2.5 2.5Glyceryl Stearate 1.0 1.0 1.0 1.0 Stearyl Alcohol 2.0 2.0 2.0 2.0 C12-15Alkyl Benzoate 14.5 14.5 14.5 13.5 Zinc Oxide (w.c.) 10.0 10.0 10.0 ZincOxide (w/o.c.) Isostearic Acid 1.0 B Glycerine 3.0 3.0 3.0 3.0 Aqua 66.561.5 51.5 51.5 Chloroacetamide 0.1 0.1 0.1 0.1 PhenylbenzimidazoleSulfonic Acid 15.0 15.0 15.0 (20% Aqua) C Xanthan Gum 0.4 0.4 0.4 0.4SPF 2 5 11 15

Examples 22-24

The standard recipe for W/O emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is incorporated into the oily phaseof the system. The additional content of zinc oxide is subtracted fromthe oily phase (C12-15 Alkyl Benzoate).

-   22 Standard recipe W/O emulsion with ZnO (w.c.)-   23 Standard recipe W/O emulsion with BEMT

24 Standard recipe W/O emulsion with ZnO (w.c.) and BEMT TABLE 9Build-up of the W/O recipes in examples 22-24 (data in %) Phase INCI 2223 24 A Cetyl PEG/PPG −10/1 Dimethicone 2.5 2.5 2.5 C12-15 AlkylBenzoate 27.00 25.00 22.00 Isostearic Acid 1.0 1.0 1.0 HydrogenatedCastor Oil 0.5 0.5 0.5 Microcrystalline Wax 1.0 1.0 1.0Bis-Ethylhexyloxyphenol 3.0 3.0 Methoxyphenyl Triazine Zinc Oxide (w.c.)5.0 5.0 B Sodium Chloride 0.5 0.5 0.5 Aqua 64.45 64.45 64.452-Bromo-2-Nitropropane-1,3-diol 0.05 0.05 0.05 SPF 2 8 13

Examples 25 to 28

The standard recipe for O/W emulsions is used in these examples. Thenanoscale zinc oxide (with coating) is introduced into the oily phase ofthe system. The additional content of zinc oxide is subtracted from theaqueous phase (Aqua). Isostearic acid is employed experimentally as asurface modifier and pH stabilizer.

-   25 Standard recipe O/W emulsion with ZnO (w.c.)-   26 Standard recipe O/W emulsion with BEMT-   27 Standard recipe O/W emulsion with ZnO (w.c.) and BEMT

28 Standard recipe O/W emulsion with ZnO (w.c.), BEMT and isostearicacid TABLE 10 Build-up of the O/W recipes in examples 25-28 (data in %)Phase INCI 25 26 27 28 A Ceteareth-15, Glyceryl Stearate 2.5 2.5 2.5 2.5Glyceryl Stearate 1.0 1.0 1.0 1.0 Stearyl Alcohol 2.0 2.0 2.0 2.0 C12-15Alkyl Benzoate 14.5 12.5 12.5 11.5 Bis-Ethylhexyloxyphenol 2.0 2.0 2.0Methoxyphenyl Triazine Zinc Oxide (w.c.) 10.0 10.0 10.0 Zinc Oxide(w/o.c.) Isostearic Acid 1.0 B Glycerine 3.0 3.0 3.0 3.0 Aqua 66.5 76.566.5 66.5 Chloroacetamide 0.1 0.1 0.1 0.1 C Xanthan Gum 0.4 0.4 0.4 0.4SPF 2 3 6 8

1. Surface-modified zinc oxides, characterized in that they have thefollowing physico-chemical characteristic data: BET surface areas: 18±5m²/g C content: 0.5 to 1.0 wt. %
 2. Surface-modified zinc oxideaccording to claim 1, which has been surface modified with a memberselected from the group consisting of: a) Organosilanes of the type(RO)₃Si(C_(n)H_(2n+1)) and RO)₃Si (C_(n)H_(2n−1)) R=alkyl, such as, forexample, methyl-, ethyl-, n-propyl-, i-propyl-, butyl- n=1-20 b)Organosilanes of the type R′_(x)(RO)_(y)Si(C_(n)H_(2n+1)) andR′x(RO)ySi(C_(n)H_(2n−1)) R=alkyl, such as, for example, methyl-,ethyl-, n-propyl-, i-propyl-, butyl- R′=alkyl, such as, for example,methyl-, ethyl-, n-propyl-, i-propyl-, butyl- R′=cycloalkyl n=1-20 x+y=3x=1,2 y=1,2 c) Halogeno-organosilanes of the type X₃Si(C_(n)H_(2n+1))and X₃Si (C_(n)H_(2n−1)) X=Cl, Br n=1-20 d) Halogeno-organosilanes ofthe type X₂(R′)Si(C_(n)H_(2n+1)) and X₂(R′)Si(C_(n)H_(2n−1)) X=Cl, BrR′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-,butyl- R′=cycloalkyl n=1-20 e) Halogeno-organosilanes of the typeX(R′)₂Si(C_(n)H_(2n+1)) and X(R′)₂Si(C_(n)H_(2n−1)) X=Cl, Br R′=alkyl,such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-, butyl-R′=cycloalkyl n=1-20 f) Organosilanes of the type (RO)₃Si(CH₂)_(m)—R′R=alkyl, such as methyl-, ethyl-, propyl- m=0,1-20 R′=methyl-, aryl (forexample —C₆H₅, substituted phenyl radicals) —C₄F₉, OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″(R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl,C₂H₄NR″″R′″″ where R″″═H, alkyl and R′″″═H, alkyl) g) Organosilanes ofthe type (R″)_(x)(RO)_(y)Si(CH₂)_(m)—R′ R″=alkyl x+y=2 =cycloalkyl x=1,2y=1,2 m=0,1 to 20 R′=methyl-, aryl (for example —C₆H₅, substitutedphenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂ —NH₂, —N₃,—SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂ —OOC(CH₃)C═CH₂—OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃, —NH—COO—CH₂—CH₃,—NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″ (R′=alkyl, aryl;R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl, C₂H₄NR″″R′″″ where R″″═H,alkyl and R′″″═H, alkyl) h) Halogeno-organosilanes of the typeX₃Si(CH₂)_(m)—R′ X=Cl, Br m=0,1-20 R′=methyl-, aryl (for example —C₆H₅,substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂ —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃—S_(x)—(CH₂)₃Si(OR)₃ —SH i)Halogeno-organosilanes of the type (R)X₂Si(CH₂)_(m)—R′ X=Cl, Br R=alkyl,such as methyl, -ethyl-, propyl- m=0,1-20 R′=methyl-, aryl (e.g. —C₆H₅,substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —S_(x)—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —SH j) Halogeno-organosilanes of the type(R)₂XSi(CH₂)_(m)—R′ X=Cl, Br R=alkyl m=0,1-20 R′=methyl-, aryl (e.g.—C₆H₅, substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂—N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH k) Silazanesof the type

R=alkyl, vinyl, aryl R′=alkyl, vinyl, aryl 1) Cyclic polysiloxanes ofthe type D 3, D 4, D 5, wherein D 3, D 4 and D 5 are understood ascyclic polysiloxanes with 3, 4 or 5 units of the type —O—Si(CH₃)₂—. E.g.octamethylcyclotetrasiloxane=D 4

m) Polysiloxanes or silicone oils of the type

R=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenylund substituted phenyl radicals, (CH₂)_(n)—NH₂, H R′=alkyl, such asC_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenyl- and substitutedphenyl radicals, (CH₂)_(n)—NH₂, H R″=alkyl, such as C_(n)H_(2n+1),wherein n=1 to 20, aryl, such as phenyl- and substituted phenylradicals, (CH₂)_(n)—NH₂, H R′″=alkyl, such as C_(n)H_(2n+1), wherein n=1to 20, aryl, such as phenyl und substituted phenyl radicals,(CH₂)_(n)—NH₂, H
 3. A process for the preparation of thesurface-modified zinc oxide according to claim 1, comprising optionallyspraying a zinc oxide with water, spraying a surface-modifying agent atroom temperature to obtain a zinc oxide sprayed with saidsurface-modifying agent, heat treating said zinc oxide at a temperatureof 50 to 400° C. over a period of 1 to 6 hours to thereby obtain asurface-modified zinc oxide.
 4. The process according to claim 3,wherein the surface-modifying agent is a member selected from the groupconsisting of: a) Organosilanes of the type (RO)₃Si(C_(n)H_(2n+1)) andRO)₃Si (C_(n)H_(2n−1)) R=alkyl, such as, for example, methyl-, ethyl-,n-propyl-, i-propyl-, butyl- n=1-20 b) Organosilanes of the typeR′_(x)(RO)_(y)Si(C_(n)H_(2n+1)) and R′x(RO)ySi(C_(n)H_(2n−1)) R=alkyl,such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-, butyl-R′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-,butyl- R′=cycloalkyl n=1-20 x+y=3 x=1,2 y=1,2 c) Halogeno-organosilanesof the type X₃Si(C_(n)H_(2n+1)) and X₃Si(C_(n)H_(2n−1)) X=Cl, Br n=1-20d) Halogeno-organosilanes of the type X₂(R′)Si(C_(n)H_(2n+1)) andX₂(R′)Si(C_(n)H_(2n−1)) X=Cl, Br R′=alkyl, such as, for example,methyl-, ethyl-, n-propyl-, i-propyl-, butyl- R′=cycloalkyl n=1-20 e)Halogeno-organosilanes of the type X(R′)₂Si(C_(n)H_(2n+1)) andX(R′)₂Si(C_(n)H_(2n−1)) X=Cl, Br R′=alkyl, such as, for example,methyl-, ethyl-, n-propyl-, i-propyl-, butyl- R′=cycloalkyl n=1-20 f)Organosilanes of the type (RO)₃Si(CH₂)_(m)—R′ R=alkyl, such as methyl-,ethyl-, propyl- m=0,1-20 R′=methyl-, aryl (for example —C₆H₅,substituted phenyl radicals) —C₄F₉, OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″(R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl,C₂H₄NR″″R′″″ where R″″═H, alkyl and R′″″═H, alkyl) g) Organosilanes ofthe type (R″)_(x)(RO)_(y)Si(CH₂)_(m)—R′ R″=alkyl x+y=2 =cycloalkyl x=1,2y=1,2 m=0,1 to 20 R′=methyl-, aryl (for example —C₆H₅, substitutedphenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂—NH₂, —N₃,—SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂ —OOC(CH₃)C═CH₂—OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃, —NH—COO—CH₂—CH₃,—NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″ (R′=alkyl, aryl;R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl, C₂H₄NR″″R′″″ where R″″═H,alkyl and R′″″═H, alkyl) h) Halogeno-organosilanes of the typeX₃Si(CH₂)_(m)—R′ X=Cl, Br m=0,1-20 R′=methyl-, aryl (for example —C₆H₅,substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂ —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅—NH—COO—CH₃₁—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃—S_(x)—(CH₂)₃Si(OR)₃ —SHi) Halogeno-organosilanes of the type (R)X₂Si(CH₂)_(m)—R′ X=Cl, BrR=alkyl, such as methyl, -ethyl-, propyl- m=0,1-20 R′=methyl-, aryl(e.g. —C₆H₅, substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —S_(x)—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —SH j) Halogeno-organosilanes of the type(R)₂XSi(CH₂)_(n)—R′ X=Cl, Br R=alkyl m=0,1-20 R′=methyl-, aryl (e.g.—C₆H₅, substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂—N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH k) Silazanesof the type

R=alkyl, vinyl, aryl R′=alkyl, vinyl, aryl 1) Cyclic polysiloxanes ofthe type D 3, D 4, D 5, wherein D 3, D 4 and D 5 are understood ascyclic polysiloxanes with 3, 4 or 5 units of the type —O—Si(CH₃)₂—. E.g.octamethylcyclotetrasiloxane=D 4

m) Polysiloxanes or silicone oils of the type

R=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenylund substituted phenyl radicals, (CH₂)_(n)—NH₂, H R′=alkyl, such asC_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenyl- and substitutedphenyl radicals, (CH₂)_(n)—NH₂, H R″=alkyl, such as C_(n)H_(2n+1),wherein n=1 to 20, aryl, such as phenyl- and substituted phenylradicals, (CH₂)_(n)—NH₂, H R′″=alkyl, such as C_(n)H_(2n+1), wherein n=1to 20, aryl, such as phenyl und substituted phenyl radicals,(CH₂)_(n)—NH₂, H
 5. A process for the preparation of thesurface-modified zinc oxides according to claim 1, comprising optionallyspraying zinc oxide with water, treating said zinc oxide with asurface-modifying agent in vapour form and then heat-treating theresulting zinc oxide at a temperature of 50 to 800° C. over a period of0.5 to 6 hours to thereby obtain a surface-modified zinc oxide.
 6. Theprocess according to claim 5, wherein the surface-modifying agent is amember selected from the group consisting of: a) Organosilanes of thetype (RO)₃Si(C_(n)H_(2n+1)) and RO)₃Si (C_(n)H_(2n−1)) R=alkyl, such as,for example, methyl-, ethyl-, n-propyl-, i-propyl-, butyl- n=1-20 b)Organosilanes of the type R′_(x)(RO)_(y)Si(C_(n)H_(2n+1)) andR′x(RO)ySi(C_(n)H_(2n−1)) R=alkyl, such as, for example, methyl-,ethyl-, n-propyl-, i-propyl-, butyl- R′=alkyl, such as, for example,methyl-, ethyl-, n-propyl-, i-propyl-, butyl- R′=cycloalkyl n=1-20 x+y=3x=1,2 y=1,2 c) Halogeno-organosilanes of the type X₃Si(C_(n)H_(2n+1))and X₃Si (C_(n)H_(2n−1)) X=Cl, Br n=1-20 d) Halogeno-organosilanes ofthe type X₂(R′)Si(C_(n)H_(2n+1)) and X₂(R′)Si(C_(n)H_(2n−1)) X=Cl, BrR′=alkyl, such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-,butyl- R′=cycloalkyl n=1-20 e) Halogeno-organosilanes of the typeX(R′)₂Si(C_(n)H_(2n+1)) and X(R′)₂Si(C_(n)H_(2n−1)) X=Cl, Br R′=alkyl,such as, for example, methyl-, ethyl-, n-propyl-, i-propyl-, butyl-R′=cycloalkyl n=1-20 f) Organosilanes of the type (RO)₃Si(CH₂)_(m)—R′R=alkyl, such as methyl-, ethyl-, propyl- m=0,1-20 R′=methyl-, aryl (forexample —C₆H₅, substituted phenyl radicals) —C₄F₉, OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″(R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl,C₂H₄NR″″R′″″ where R″″═H, alkyl and R′″″═H, alkyl) g) Organosilanes ofthe type (R″)_(x)(RO)_(y)Si(CH₂)_(m)—R′ R″=alkyl x+y=2 =cycloalkyl x=1,2y=1,2 m=0,1 to 20 R′=methyl-, aryl (for example —C₆H₅, substitutedphenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂—NH₂, —N₃,—SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂ —OOC(CH₃)C═CH₂—OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃, —NH—COO—CH₂—CH₃,—NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH —NR′R″R′″ (R′=alkyl, aryl;R″═H, alkyl, aryl; R′″═H, alkyl, aryl, benzyl, C₂H₄NR″″R′″″ where R″″═H,alkyl and R′″″═H, alkyl) h) Halogeno-organosilanes of the typeX₃Si(CH₂)_(m)—R′ X=Cl, Br m=0,1-20 R′=methyl-, aryl (for example —C₆H₅,substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂ —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH i)Halogeno-organosilanes of the type (R)X₂Si(CH₂)_(m)—R′ X=Cl, Br R=alkyl,such as methyl, -ethyl-, propyl- m=0,1-20 R′=methyl-, aryl (e.g. —C₆H₅,substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂, —N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —S_(x)—(CH₂)₃Si(OR)₃, wherein R can be methyl-, ethyl-,propyl-, butyl- —SH j) Halogeno-organosilanes of the type(R)₂XSi(CH₂)_(m)—R′ X=Cl, Br R=alkyl m=0,1-20 R′=methyl-, aryl (e.g.—C₆H₅, substituted phenyl radicals) —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃,—O—CF₂—CHF₂—NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂—N—(CH₂—CH₂—NH₂)₂—OOC(CH₃)C═CH₂ —OCH₂—CH(O)CH₂ —NH—CO—N—CO—(CH₂)₅ —NH—COO—CH₃,—NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si(OR)₃ —S_(x)—(CH₂)₃Si(OR)₃ —SH k) Silazanesof the type

R=alkyl, vinyl, aryl R′=alkyl, vinyl, aryl 1) Cyclic polysiloxanes ofthe type D 3, D 4, D 5, wherein D 3, D 4 and D 5 are understood ascyclic polysiloxanes with 3, 4 or 5 units of the type —O—Si(CH₃)₂—. E.g.octamethylcyclotetrasiloxane=D 4

m) Polysiloxanes or silicone oils of the type

R=alkyl, such as C_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenylund substituted phenyl radicals, (CH₂)_(n)—NH₂, H R′=alkyl, such asC_(n)H_(2n+1), wherein n=1 to 20, aryl, such as phenyl- and substitutedphenyl radicals, (CH₂)_(n)—NH₂, H R″=alkyl, such as C_(n)H_(2n+1),wherein n=1 to 20, aryl, such as phenyl- and substituted phenylradicals, (CH₂)_(n)—NH₂, H R′″=alkyl, such as C_(n)H_(2n+1), wherein n=1to 20, aryl, such as phenyl und substituted phenyl radicals,(CH₂)_(n)—NH₂, H
 7. A cosmetic preparation comprising a dermatologicallyacceptable carrier and the surface-modified zinc oxide of claim
 1. 8. Acosmetic preparation comprising a dermatologically acceptable carrierand the surface-modified zinc oxide of claim
 2. 9. A sunscreenpreparation comprising a dermatologically acceptable carrier and thesurface modified zinc oxide of claim
 1. 10. A sunscreen preparationcomprising a dermatologically acceptable carrier and the surfacemodified zinc oxide of claim
 2. 11. The sunscreen preparation accordingto claim 9, wherein the dermatologically acceptable carrier is a memberselected from the group consisting of octocrylene, ethylhexylmethoxycinnamate, phenylbenzimidazole sulfoinc acid, andbis-ethylhexyloxy methoxyphenyl triazine.